1. Field of the Invention
The invention relates to a chain for a sawing device. The invention also relates to a motor-driven sawing device.
2. Description of the Related Art
For the processing of tree trunks, there are known harvesting devices used, such as feller heads, which cut the tree trunk and grip it and fell it in a controlled manner. The head is normally fixed at the end of a boom assembly in a working machine which is movable on a terrain by means of wheels or a crawler. Such a device is disclosed in patent publication U.S. Pat. No. 5,979,518 in which the cutting is effected by means of a movable chain saw. For supporting the tree trunk, the head is also equipped with grapple means which can be swivelled in relation to a frame structure, normally pairwise on different sides of the tree trunk. A feller device without grapples is also known from patent publication U.S. Pat. No. 4,848,424, in which a sawing chain encircles a support plate moving in a linear manner in the frame. Another such device is disclosed in patent publication U.S. Pat. No. 4,462,439, in which the saw flange, encircled by the chain, is rotated around a vertical axis. The support plate and the saw flange support the tree trunk to be cut during the sawing. The cutting can also be executed with a rotating blade wheel, wherein known feller heads are equipped with a stationary plate above the blade wheel. The weight of the cut trunk is also supported on the plate during transfers. The edge of the blade wheel is provided with high teeth which cut a hole in the trunk for the blade wheel and the plate. The trunk is supported in a vertical position by means of grapple means.
For cutting of the trunk, the blade wheel of the sawing device must be made considerably larger than the diameter of the trunk, which results in a large mass and size. The heavy blade wheel is also slow to accelerate and to stop, wherein to speed up the working, the blade wheel is normally continuously in operation, which may lead to risk situations. During and after the cutting, the trunk is supported to the plate above the blade wheel, which plate must be made very strong. The slot to be sawn must be made wide, wherein the output capacity required of the device increases. The manipulation of the heavy and bulky feller head is very difficult.
Therefore, it is preferable to use a saw chain which can be installed in different ways to encircle various flange structures and whose mass is considerably smaller than that of a blade wheel. The chain can thus be rotated only when it is necessary and be stopped at other times, wherein the saw engine does not continuously drive pressurized medium in the working machine.
The tree trunk causes a considerable load on the supporting saw flange. The maximum thickness of the saw flange is determined by the width of the slot formed at the sawing point. The front edge of the saw flange, which also supports the saw chain, must not be thicker than the saw chain, to make the saw flange penetrate into the slot. The saw flange can also be wedge-shaped, but this increases the required feed force of the saw flange and may increase the forces effective on the saw chain. The result is, for example, that the size of tree trunks to be processed by the felling device must be limited.
It is an aim of the present invention to eliminate the drawbacks presented above and to provide a safe harvesting device. Another aim is to provide a sawing device with a sufficient service life, particularly for feller heads. In particular, an aim is to provide, by simple means, a widened chain which makes it possible to use a simple and durable flange structure in a sawing device. To achieve these aims, the chain for a sawing device according to the invention is presented. The motor-driven sawing device according to the invention is also presented.
The essential principle in the invention is particularly a widened chain and its assembly of primarily standard parts which are also used for assembling a normal-width chain for a sawing device. A considerable advantage is thus that said standard parts, particularly the links in the chain, are easily available parts, thereby reducing the manufacturing costs of the chain. Another advantage is that the necessary auxiliary parts are parts which are easy to manufacture at a low cost. It is not necessary to store several different links for different chain widths.
By applying the same principle, the chain can be made to have a desired width, wherein cutting teeth are provided at its whole width. By means of the wide saw chain, the sawing slot thus becomes wider for a thicker and stronger flange structure used as the support plate. The support plate can be made of a material having good gliding properties, and it can have an even thickness. The rigid flange structure is less sensitive for deformations which are due to loading and cause problems in the path of the chain.
To enlarge the slot, it is also possible to place, for example, two known chains next to each other. In this case, also the need for power supply is doubled. Problems are also caused by different wearing and separate tensioning of the chains. The slot and the saw flange become unnecessarily large, if the chains must be placed apart from each other to prevent collisions. By using the chain according to the invention, the width of the chain and thereby the slot can be changed in steps consisting of the width of two adjacent links. In this way, the structure of the saw flange does not become unnecessarily thick or complex.